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Final Research Plan

Final Research Plan for Peripheral Artery Disease in Adults: Screening With the Ankle Brachial Index

Recommendations made by the USPSTF are independent of the U.S. government. They should not be construed as an official position of the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.

This systematic review will examine the evidence on the effectiveness of screening in generally asymptomatic populations for peripheral artery disease (PAD) in order to improve cardiovascular and PAD-specific morbidity and mortality. A concurrent systematic review on the use of nontraditional risk factors in cardiovascular disease (CVD) risk assessment will address the evidence on the effects of resting ankle brachial index (ABI) on 1) the discrimination or calibration of multivariate risk prediction models when used in addition to traditional CVD risk factors, 2) CVD risk reclassification, and 3) CVD health outcomes. Together, these two systematic reviews will serve as the basis for the USPSTF recommendation on screening for PAD.

Analytic Framework

Abbreviation: ABI=ankle brachial index.

Text Description.

Figure 1 is the analytic framework that depicts the five Key Questions (KQs) to be addressed in the systematic review. The figure illustrates how screening generally asymptomatic adults for peripheral artery disease (PAD) with the ankle brachial index (ABI) may reduce mortality, cardiovascular morbidity, PAD morbidity, and quality of life (KQ 1). The figure also depicts the diagnostic accuracy of ABI as a screening test for PAD (KQ 2) and the harms of screening (KQ 3). KQ 4 depicts whether treatment of screen-detected or generally asymptomatic adults with PAD or abnormal ABI improves the patient health outcomes evaluated in KQ 1 and if there are harms associated with treatment (KQ 5).

Key Questions to Be Systematically Reviewed

  1. Is screening for PAD in generally asymptomatic adults* with the ABI effective in reducing CVD or PAD morbidity (e.g., impaired ambulation or amputation) or mortality?
    1. Does the effectiveness of screening for PAD vary by subpopulations at greater risk for PAD?
  2. What is the diagnostic accuracy of the ABI as a screening test for PAD in generally asymptomatic adults*?
    1. Does the diagnostic accuracy of screening with the ABI vary by subpopulations at greater risk for PAD?
  3. What are the harms of screening for PAD with the ABI?
    1. Do the harms of screening for PAD vary by subpopulations at greater risk for PAD?
  4. Does treatment of screen-detected or generally asymptomatic adults* with PAD or an abnormal ABI lead to improved patient health outcomes?
    1. Does the effectiveness of treatment vary by subpopulations at greater risk for PAD?
  5. What are the harms of treatment of screen-detected or generally asymptomatic adults* with PAD or an abnormal ABI?
    1. Do the harms of treatment vary by subpopulations at greater risk for PAD?

Contextual Questions

Contextual questions will not be systematically reviewed and are not shown in the Analytic Framework.

  1. In primary care, what proportion of adults with an abnormal ABI are generally asymptomatic*?
    1. What proportion of generally asymptomatic adults* with an abnormal ABI receive additional diagnostic testing?
    2. What proportion of generally asymptomatic adults* with an abnormal ABI have an ABI greater than 1.40?
    3. What proportion of generally asymptomatic adults* with an ABI  greater than 1.40 have PAD?
  2. What proportion of generally asymptomatic adults* with PAD or an abnormal ABI have lower extremity functional impairment? What is the degree of lower extremity functional impairment, and how does it compare to impairment in patients with reported symptoms (e.g., claudication)?
  3. Do generally asymptomatic adults* with PAD or an abnormal ABI have the same risk of global CVD events as symptomatic adults with PAD?

* Adults without lower extremity symptoms or with vague symptoms not attributed to PAD.
Defined as an ABI of ≤0.90 or >1.40.

Research Approach

The Research Approach identifies the study characteristics and criteria that the Evidence-based Practice Center will use to search for publications and to determine whether identified studies should be included or excluded from the Evidence Review. Criteria are overarching as well as specific to each of the key questions (KQs).

  Included Excluded
Population KQs 1–3: Unselected or community-dwelling, generally asymptomatic adults*

KQs 4, 5: Screen-detected or generally asymptomatic adults with PAD or an abnormal ABI

A priori subpopulations at greater risk for PAD will be examined based on the following factors: age (particularly ≥65 years), sex, race/ethnicity, diabetes, smoking, and hypertension status

Symptomatic adults; study populations consisting exclusively of adults with known CVD or severe chronic kidney disease (stages 4 and 5)
Setting Primary care and outpatient settings (i.e., ambulatory care) Vascular surgery clinics (KQs 1, 2); hospital/inpatient settings
Disease/Condition Lower extremity PAD secondary to atherosclerosis Other anatomic locations for vascular disease (e.g., coronary artery stenosis, abdominal aortic aneurysm)
Screening Resting ABI History taking, physical examination, questionnaires, digital subtraction arteriography (DSA), duplex ultrasonography, magnetic resonance angiography (MRA), computed tomographic angiography (CTA), toe pressure measurement, treadmill testing (exercise ABI), pulse oximetry, near-infrared spectroscopy, and all invasive diagnostic testing
Treatment or management interventions
  • Pharmacologic or lifestyle interventions primarily aimed at CVD reduction: interventions for smoking cessation, cholesterol-lowering therapy, diet and exercise (with or without weight loss), blood pressure control, and antiplatelet therapy
  • Exercise or physical therapy interventions aimed at improving lower limb function
  • Vitamins or nutritional or herbal supplements
  • Interventions aimed only at symptomatic persons or patients with critical limb ischemia: pharmacologic symptom management (pentoxyfylline, cilostazol, prostaglandins); nonpharmacologic symptom management; and revascularization (angioplasty, thrombolytics, stenting, bypass)
Comparisons KQ 1: No screening

KQ 2: Reference standard (DSA, diagnostic imaging of atherosclerosis [e.g., MRA, CTA]) or degree of impaired blood flow (e.g., duplex ultrasonography)

KQ 4: True control group (receives placebo, no intervention, or usual care); intervention/treatment at later or symptomatic stage of disease (vs. earlier or asymptomatic stage)

 
Outcomes KQ 1: Cardiovascular morbidity (myocardial infarction, cerebral vascular accident), PAD morbidity (ambulation impairment, amputation), or mortality (all-cause, PAD-related, or CVD-related); health-related quality of life

KQ 2: Sensitivity, specificity, positive and negative predictive value for PAD, and incidence or prevalence

KQ 4: Patient health outcomes (listed above for KQ 1)

  • Surrogate markers for atherosclerosis, including imaging (e.g., carotid intima-media thickness) or biochemical markers (e.g., high-sensitivity C-reactive protein)
  • Patient satisfaction
  • Cost-related outcomes (for screening and treatment)
  • Intermediate cardiovascular outcomes (e.g., blood pressure, cholesterol); behavior changes (e.g., smoking cessation, physical activity level); intermediate measures of lower limb function (e.g., 6-minute walking test, lower extremity strength)
  • Change in ABI
Harms KQ 3: Adverse outcomes related to ABI test (diagnostic inaccuracy) or harms of subsequent testing

KQ 5: Serious adverse events (e.g., death, serious adverse drug reaction) or unexpected medical attention (e.g., emergency department visit, hospitalization)

Patient satisfaction
Study designs KQs 1, 4: Good-quality systematic reviews and randomized or clinically controlled trials

KQ 2: Good-quality systematic reviews and diagnostic accuracy studies

KQs 3, 5: Good-quality systematic reviews, randomized or clinically controlled trials, and cohort or case-control studies

Poor-quality studies based on established design-specific quality criteria

KQ 2: Case-control studies of diagnostic accuracy

KQ 4: Studies with less than 3 months of followup

Countries Economically developed countries, defined as member countries of the Organisation for Economic Co-operation and Development (2015): Australia, Austria, Belgium, Canada, Chile, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Israel, Italy, Japan, Korea, Luxembourg, Mexico, Netherlands, New Zealand, Norway, Poland, Portugal, Slovak Republic, Slovenia, Spain, Sweden, Switzerland, Turkey, United Kingdom, and United States
  • Studies performed in countries with populations not similar to those of the United States
  • Countries that are not a member of the Organisation for Economic Co-operation and Development
Language English only Non-English languages

* Adults without lower extremity symptoms or with vague symptoms not attributed to PAD.
Defined as an ABI of ≤0.90 or >1.40.
The condition definition for PAD would ideally be confirmed by diagnostic imaging (MRA, CTA, or DSA); however, the review will include trials that recruit participants with an abnormal ABI.

Response to Public Comment

A draft research plan was posted on the USPSTF Web site for public comment from March 24 to April 20, 2016. This review will address screening in unselected populations according to USPSTF methodology but will also review the evidence for subpopulations at greater risk for PAD based on age (particularly ≥65 years), sex, race/ethnicity, diabetes, smoking, and hypertension status. Based on the comments it received, the USPSTF revised the eligibility criteria to also include studies in adults with diabetes. Adults with known coronary artery disease or severe chronic kidney disease will continue to be excluded because their high risk places them outside of the screening paradigm. Comments suggested that two points could benefit from additional clarification. First, the addition of “generally asymptomatic adults” as well as “screen-detected adults” to KQs 4 and 5 (treatment effectiveness and harms) is intended to expand rather than restrict the number of eligible trials. Second, all of the PAD morbidity outcomes (e.g., impaired ambulation or amputation) and CVD outcomes for KQ 1 will be analyzed and reported individually, not as part of a single composite outcome.

Current as of: June 2016

Internet Citation: Final Research Plan: Peripheral Artery Disease in Adults: Screening With the Ankle Brachial Index . U.S. Preventive Services Task Force. June 2016.
https://www.uspreventiveservicestaskforce.org/Page/Document/final-research-plan/peripheral-artery-disease-in-adults-screening-with-the-ankle-brachial-index

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